The present invention relates to a system for generating stitch pattern signals for use in electronic sewing machines in which the information relating to the stitching needle movement and to the feeding dog movement and stored in a static memory is read out in timed relation to the rotation of the machine main shaft and fed to drive means for controlling the bight and feed to enable the machine to form stitch patterns.
In recent years, sewing machines have been developed in which stitch pattern information is electronically stored in a memory to form stitch patterns without resorting to a mechanical cam device. For example, an electronic sewing machine is known in which a tremendous amount of stitch pattern information is stored in a read-only memory (ROM). Fabrication of such a read-only memory requires a cumbersome procedure of storing the required information in the correct order, so that the memory is not adapted for quantity production unlike other logical elements. For use as means for storing sewing machine stitch pattern information, different read-only memories must be prepared for the desired number of different patterns to be stored. Thus how to store the required information in a read-out memory of the smallest possible capacity is commercially most significant. The electronic sewing machine disclosed in Japanese Pat. Application Disclosure No. 37554/1975 includes such a read-only memory for storing stitch pattern information. For the formation of a stitch pattern, the read-only memory has stored therein the bight information for the needle and the feed information for the feed dog which are arranged as a pair in the order of stitch forming, such that the stored information is read out as arranged in the memory by addressing the memory with the output of a counter which counts as the machine shaft rotates. With the disclosed system, the pattern forming operation which was conventionally stored in a mechanical memory as with use of a cam or paper tape is similarly stored in the electronic memory merely substituted for the mechanical means. Stated another way, the electronic memory in such prior art systems is in reality little more than an electronic analogue of the mechanical memory in conventional mechanical cam controlled sewing machines. In such prior art electronic systems, the same amount of information must be stored in the memory, merely in another form, as is stored in the prior art mechanical memories. Thus the read-only memory is not so adapted as to store the required information with the smallest possible capacity. This will be described with reference to FIG. 1 showing a tulip pattern which is most frequently used as a symmetric sewing machine stitch pattern. The illustrated pattern is symmetrical with respect to the stitch No. 16. Table 1 below shows the bight position cordinate and feed increment for each stitch.
Table 1 ______________________________________ Bight Feed Bight Feed Stitch position incre- Stitch position incre- No. cordinate ment No. cordinate ment ______________________________________ 1 -15 +8 16 +15 +6 2 -15 +8 17 +9 +3 3 -15 +8 18 +15 +3 4 -15 -8 19 +9 -2 5 -11 -6 20 +3 -3 6 -7 -3 21 -1 -5 7 -3 +8 22 -3 0 8 -7 +10 23 -11 +10 9 -11 0 24 -7 +8 10 -3 -5 25 -3 -3 11 -1 -3 26 -7 -6 12 +3 -2 27 -11 -8 13 +9 +3 28 -15 +8 14 +15 +3 29 -15 +8 15 +9 +6 30 -15 +8 ______________________________________
It is seen that the bight data is symmetrical with respect to stitch No. 16, whereas with respect to the feed data, the data, for example, for stitch No. 17 next to No. 16 does not correspond to the data for No. 15 which is the first stitch before No. 16 but corresponds to the data for No. 14 which is the second stitch before No. 16. This is characteristic of the sewing operation of the machine by which stitches are formed by the alternation of the bight movement of the needle and the feed movement of the dog. The above-mentioned embodiment uses a system in which the combination of bight data and feed data for each stitch is prepared and the whole stitch pattern information is stored in ROM in the order of stitch formation. As far as this system is concerned, however, it is by no means possible to form a symmetrical pattern with a memory of reduced capacity in which only one half of the overall pattern information is stored, such that for the formation of the remaining half of the pattern, the stored information is read out in the reverse order. Thus the information of the whole stitch pattern must be stored.
This is also the case with the shell pattern shown in FIG. 2 which is similarly symmetrical with respect to the stitch No. 16. Table 2 shows the bight position cordinate and feed increment for each stitch of this pattern.
Table 2 ______________________________________ Bight Feed Bight Feed Stitch Position incre- Stitch position incre- No. cordinate ment No. cordinate ment ______________________________________ 1 -15 +1 16 +15 +1 2 -5 +1 17 +1 +1 3 -11 +1 18 +15 +1 4 +4 +1 19 +1 +1 5 -7 +1 20 +14 +1 6 +8 +1 21 0 +1 7 -4 +1 22 +13 +1 8 +11 +1 23 -2 +1 9 -2 +1 24 +11 +1 10 +13 +1 25 -4 +1 11 0 +1 26 +8 +1 12 +14 +1 27 -7 +1 13 +1 +1 28 +4 +1 14 +15 +1 29 -11 +1 15 +1 +1 30 -5 +1 ______________________________________
Storing the bight data and feed data of each stitch for the whole of such a pattern involves a great waste in the memory capacity because the feed data, which is of one kind, must be stored for all stitches.
Furthermore, the smocking stitch shown in FIG. 3 and the feather stitch shown in FIG. 4 involve the bight position cordinates and feed increments given in Table 3 and Table 4 respectively.
______________________________________ Table 3 Table 4 Bight Feed Bight Feed Stitch position incre- Stitch position incre- No. cordinate ment No. cordinate ment ______________________________________ 1 -15 +10 1 -15 +10 2 -5 -10 2 -5 +10 3 +5 +10 3 +5 -10 4 +15 +10 4 +15 +10 5 +5 -10 5 +5 +10 6 -5 +10 6 -5 -10 1' -15 +10 1' -15 +10 2' -5 -10 2' -5 +10 : : : : : : : : : : : : ______________________________________
These tables indicate that the above-mentioned stitches are provided by a combination of the bight data for the mending stitch shown in FIG. 5 and the feed data for the stretch stitch shown in FIG. 6. Tables 5 and 6 show bight position coordinates and feed increments for the mending stitch and stretch stitch which are very fundamental.
______________________________________ Table 5 Table 6 Bight Feed Bight Feed Stitch position incre- Stitch position incre- No. cordinate ment No. cordinate ment ______________________________________ 1 -15 +2 1 0 +10 2 -5 +2 2 0 +10 3 +5 +2 3 0 -10 4 +15 +2 1' 0 +10 5 +5 +2 2' 0 +10 6 -5 +2 12 3' 0 -10 ______________________________________
Thus the smocking stitch or feather stitch is provided by the combination of the bight data given in Table 5 (namely: -15, -5, +5, +15, +5, -5) and the feed data (+10, +10, -10) given in Table 6. Even in these cases, nevertheless, the conventional memory system requires that the pattern information for each stitch pattern be stored. It therefore follows that the inefficient use of memory capacity increases with the increase in the number of kinds of patterns.